Method of oxidizing sulfur dioxide to sulfur trioxide



Patented Apr. 15, 1947 METHOD OF OXIDIZING SULFUR DIOXIDE T SULFURTRIOXIDE Edgar F. Rosenblat't, East Orange, and Louis Pollen,.Unionville, N. J., assignors to Baker & Company, Inc., Newark, N. J., acorporation of New Jersey No Drawing. Application May 23, 1942,

, Serial No. 444,266

1 This invention relates generally to catalytic processes and isconcerned with the oxidation of sulphur dioxide to sulphur trioxide inthe contact process of manufacturing sulphuric acid,

-wherein sulphur dioxide is contacted with oxygen, as contained forinstance in air or other gaseous medium, at elevated temperature in thepresence of a catalyst to produce sulphur trioxide. More specifically,the invention deals with the catalytic oxidation of $02 to $03 by meansof a supported platinum metal catalyst.

Catalysts embodying platinum metals as catalytically active materialcomprise two broad groups. In one group the catalyst consists of theplatinum metal in the form of wire or powder, as for instance in theform of wire gauze, and in the other group the catalyst consists of asupport carrying platinum metal on its surface in one form or another.Catalysts of the former group are not suitable for the production ofsulphuric acid by the contact process, and all catalysts for theoxidation of S02 to SO: inthe contact process of manufacturing sulphuricacid, therefore, consist of the supported type of catalyst. While theemployment of supported catalysts embodying as catalyst metal a metal ofthe platinum group other than platinum itself is known, no practical useof such catalysts has been made in the oxidation of S02 to S0: so thatsuch catalysts for the manufacture of sulphuric acid have been limitedin practice to supported platinum catalysts.

Efforts have been made to increase the activity and performance ofsupported platinum catalysts by associating with the catalyst othersubstances such as base metal compounds serving as promoters or the likeor by improving the methods of epositing he catalytic platinum on thesupport.

We have found, however, that the catalytic activity of such supportedcatalysts for the oxidation of S02 to S03 can be improved substantiallyby depositing on supports platinum in association with palladium.

The improved catalytic efiiciency and perform- 4 Claims. ((31. 23-175)ance in the oxidation of S02 130803 of such supported catalysts,comprising a combination of platinum and palladium, is particularlysurprising in that palladium as such when deposited on a carrier ha nocatalytic activity in the oxidation of SOzto S03 in the temperaturerange of sulphuric acid plant operations.

The carrier of the catalyst according to this invention may comprise anysuitable material such as aluminum oxide, magnesium sulphate, silicagel, asbestos, etc. The metals platinum and palladium may be depositedon the carrier in any suitable manner as, for instance, by dissolvingcompounds thereof in a solvent, aqueous or organic, bringing the carrierand the solvent in contact, and decomposing such compounds by reducingagents or under heat. The deposition of platinum and palladium in suchmanner may take place by depositing first one metal and then another,although simultaneous deposition thereof from one solvent is to bepreferred. The platinum and palladium are deposited in a thoroughcombination, the exact nature of which has not been ascertained as towhether such combination represents a mixture or an alloy of such metalsor a mixture of metal and oxide, although from the appearance of thecatalyst and the general chemical behavior of the metals it appearsprobable that at least a large part of the palladium is present in theform of an oxide thereof whereas the platinum is largely present inmetallic form.

The increased catalytic eiiiciency of the cata lysts according to thisinvention will be apparent from the specific examples which we are aboutto give, the metal or metals being deposited in a uniform layer on thesurface of a carrier. In all cases the catalyst metal was deposited inlike manner by employing the method more particularly described in ourco-pending application Serial No. 438,568 filed April 11, 1942, wherebya compound of platinum and palladium is dissolved in an organic solventof low volatility such as fish oil or the like, and the catalyst metalis deposited 3 on the carrier by decomposition of the compounds underheat. In the examples the supports consist of magnesium sulphate andaluminum oxide 1. The method of oxidizing sulphur dioxide to sulphurtrioxide, comprising reacting sulphur dioxide and oxygen at reactiontemperatures in pellets, respectively. the presence of a supportedcatalyst comprising Table Catalyst Metal Catalyst Chan ber Compositionclafglglst Temperature, C. Per cent per cent Support 0 wt on Maxismn Percent Per cent i Entrance i Exit to 80 Pt Pd Temp. Temp Temp.

........ 100 0.33 MgSOin 315 340 339 None 100 0.33 ld0. 395 401 395Trace 100-" 0. 30 do 310 490 450 92.5

90 .10 0. 30 dO. 304 496 439 93.5 75 0.130 -dO 306 472 432 95. 9 50 50'0.30 do 312 470' 446 93. 9 65 35 07 do 311 477 413 95.3 75 25 0. 60A1201- 305 489 406 97. 2 65 0. 60 .do 301 481 409 96.7 25 75 0. 60 do330 498 482 88. l 10 90 0. 60 d0 329 50].: 500 78. 8'

The above table is intended to merely give a few representativeexperiment serving to illustrate the increase in efiiciency produced bycombining platinum with palladium in the production of supportedcatalysts for the oxidation of $02 to S03. The exact ratio of platinumtopalladium does not appear to be generally critical for the productionof supported catalysts according to this invention, in that even smallquantities of palladium, such as below 10%, have a favorable eifect onthe conversion efficiency and in that. even large quantities ofpalladium such as in. excess of 50% palladium may be utilized for theproduction of favorabl results. Catalysts relatively rich in palladium,such as catalysts con taining substantially more than 50% palladium, arehowever inferior in conversion efiiciency to catalysts relatively richin platinum. Palladium is considerably less expensive than platinum sothat'the production of a highly active supported catalyst embodyingpalladium is not only advantageous from a conversion point of View butalso from a cost point of view. While, therefore, catalysts containingsmall quantities of palladium as Well as catalysts containing largequantities of palladium furnish advantageous results, we have throughthe catalyst bed with a velocity of 6000 volumes of gas mixture at 0 C.and 760 'mm. Hg pressure per volume of catalyst per hour.

that weclaim is:

a carrier having deposited thereon a thin layer of platinum andpalladium containing from about to 90% platinum and from about 10% to50% palladium.

2. The method of oxidizing sulphur dioxide to sulphur trioxide,comprising reacting sulphur dioxide and oxygen at reaction temperaturesin aluminum oxide.

EDGAR F. ROSENBLATT.

LOUIS POLLEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS found that from the point of view of plant oper-Number Name Date ations the most advantageous catalyst comprises2,076,953 Lacy Apr. 13, 1937 from about 10% to about 50% palladium rela-1,314,952 Elli Sept. 2, 1919 tive to about 90% to about 50% platinum andWe 2,330,664 Bennett Sept. 28, 1943 recommend in particular catalystscomprising 657,004 Pier Aug, 8 1900 from about 20% to about 40%palladium relative to from about 80% to about platinum. r FOREIGNPATENTS In the experiments above reported thecatalysts Number CountryDate were tested in an adiabetic catalyst chamber cor- 354,500 BritishAug. 13, 1931 responding to the first converter of a two-con- 6,448British 1905 verter system in the oxidation of S02 to $03; the 440,338German Feb. 16, 1926 gas mixture contained 8% S02 and was passed 60OTHER REFERENCES Mfg of Acids and Alkalies, Lunge and Gunnings, vol. IV,Mfg of sulfuric acid (contact proc. ess) Miles page 123. (Copy in Div.59.)

